I'm going back to the basic question which the OP posted.
Fit Aico, not FireAngel. I have never had a call-back to an Aico unit. To be fair, I've never fitted FireAngel, but I wouldn't risk it given many online comments about their unreliability/difficulty in pairing.
As a side-note, before the new Scottish regs came into play, whereby RF fully wireless alarms were permitted, I installed a few "hybrid" systems whereby there was a mains unit in the hall, and 10-year battery alarms elsehwere with RF modules in each unit. Thus, there was a mains supplied unit with RF connectivity (permitted) and other units purely on battery with RF...I did enquire of the LA in all cases and they had no idea, didn't care...and of course these systms are now legitimised by the current regs. Those early installations are all still working fine...and they were all Aico. I test them annually and they just keep on working. The reason for the hybrid nature was to avoid damage to period cornicing and other features.
I did fit another brand recently, customer supplied, and they seemed fine, just as easy to install as Aico, just as easy to pair, and quite a bit smaller and cheaper. I'll try to find out what make they are and post later.
My main reason for this post is to say that prices vary enormously for the Aico units, so it is worth shopping around. Indeed, from some suppliers, the smoke with the RF module included and already installed, is cheaper than the basic unit was during lockdown and before...lockdown was a supply chain problem too.
Today, I checked the price from my 2 main suppliers of Aico units, and compared the price of just one item, the Aico Ei650RF.
On one site, the price is £92.83 inc. VAT and claims a price reduction of £40.84...
On another site, and the one I use now, the same unit is showing at £57.30 inc. VAT.
Both claim that they are ready to go, with RF module included. From my experience, both are.
On that basis, fit Aico, wireless, fit and forget...or add an extra interrogation/reporting module and other accessories to suit your needs.
Aha! I hear you ask, which site was the cheaper of the two?
Well, that'll cost you £30!
LOL!
Seriously...Edwardes was the cheaper site...but always shop around.